An ideal operational amplifier amplifies the difference in voltages applied to its two input terminals. If the input voltages are equal, then the ideal output voltage of the amplifier is zero. In practical operational amplifiers, however, the output is often not zero due to an unbalanced differential pair in the operational amplifier. This non-zero output can be modeled as an offset voltage. If the offset voltage is constant over the operational range of the amplifier then compensation can be accomplished using another voltage of the same magnitude and opposite polarity. The offset voltage, however, depends on transconductance gain of the differential pair, and the transconductance gain can vary with changes in temperature. This can result in an offset voltage that is not constant.